1. Field of the Invention
An object of the present invention is a method by which it is possible to secure the transmission of data elements between a sensor delivering pulses and a recorder processing these pulses, as well as a system to implement the method.
The field of application that is a particular object of the invention is that of chronotachographs used in heavy road vehicles to verify their speed of movement and check compliance by truck drivers with the regulations on time.
2. Description of the Prior Art
At present, chronotachographs consist essentially of a tachometric sensor that transmits one or more pulses by a differential electrical link to a recorder, for example a disk, each time that the wheels of the heavy road vehicle have made one revolution. By examining the period of repetition of the recorded pulses, the speed of the vehicle in motion is deduced.
The sensor and the recorder are generally separated by a distance of 2 to 10 meters.
For the time being, there is no security system provided on existing chronotachographs. This enables all types of fraudulent activity: it is possible in particular to set up a parallel connection of a false sensor on the link between the existing sensor and recorder. This false sensor modifies (in this case reduces) the number of pulses transmitted.
The aim of the present invention is to secure the transmission of data elements between the sensor and the recorder, and to do this at several levels:
First of all it is sought to secure the transmission at the level of the link, on the one hand to prevent false information from being transmitted to the recorder and, on the other hand, to prevent a falsified sensor from being connected instead of the one that has been certified by the checking organization.
More specifically, an aim of the invention is to detect and record any attempt to falsify the link between the sensor and the recorder.
Then, with regard to the information transmitted, the invention is designed to prevent the data elements of the sensor from being modified.
The present invention may be extended to any type of transmission between a sensor delivering pulses and a recorder in charge of processing them.